Phase domain modelling and simulation of large-scale power systems with VSC-based FACTS equipment.
PhD thesis, University of Glasgow.
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Most of the analysis techniques available for planning and operation of multiphase power systems are based upon the assumption that the network operates under perfectly balanced conditions. The advantage of this assumption from the modelling view point is that only one phase of the three phase system needs to be considered for analysis, resulting in a reduced size of the problem at hand. However, the phase frame of reference offers a more general representation for the solution of power system problems than the frame of reference provided by the sequences. The former can accommodate networks containing any degree of unbalance whilst the latter is only applicable to power networks exhibiting perfect or near-perfect impedance balance between phases.
The thesis reports on the development of steady state and time domain models of Flexible AC Transmission System (FACTS) controllers in the natural framework of electric systems, i.e. namely the phase co-ordinates domain. The FACTS equipment selected for analytical development in this research are: the static synchronous compensator (STATCOM), the static synchronous series compensator (SSSC), the unified power flow controller (UPFC) and the high-voltage direct current (HVDC). These power electronics-based controllers have the voltage source converter as their main constituent. The combined solution of both steady state and dynamic power flow equations pertaining to the VSC-based FACTS controllers and the power network are fully described in the thesis.
The steady-state mathematical models of VSC-based FACTS controllers are formulated in nodal form using the frame of reference of the phases. Guidelines for their implementation into two distinct power flows algorithm namely, the Newton-Raphson in polar co-ordinates and the Newton-Raphson in rectangular coordinates are given. For the purpose of long-term dynamic assessment, a simultaneous solution using implicit trapezoidal integration method with Newton iteration is used to solve the set of differential-algebraic equations of generating plants and network components. In order to assess both the steady state and the dynamic behaviour of the models developed, a comprehensive, newly developed integrated software environment is used.
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